Conventional vehicle braking systems include those having a brake pedal operatively connected to a booster which is operatively connected to a brake apply master cylinder. In one known system, the brake apply master cylinder includes a primary brake apply piston (having attached seals) and a secondary brake apply piston (having attached seals) arranged in tandem within the bore of the brake-apply-master-cylinder body. Systems having annular lip seals supported by the brake-apply-master-cylinder body (instead of piston-attached seals) are also known. It is noted that seals supported by the brake-apply-master-cylinder body are known as fixed seals, and seals attached to the piston are referred to as moving seals.
During brake apply, the primary brake apply piston moves longitudinal forward (toward the closed front end of the bore of the brake-apply-master-cylinder body) which compresses a first spring which moves the secondary brake apply piston longitudinally forward which compresses a second spring seated against the closed front end of the bore. Such longitudinally forward movement compresses the brake fluid in the primary brake circuit which is in fluid communication with the bore between the primary and secondary brake apply pistons and compresses the brake fluid in the secondary brake circuit which is in fluid communication with the bore longitudinally forward of the secondary brake apply piston. The pressure is the same in both braking circuits.
During brake release, the springs return the primary and secondary brake apply pistons to their rest positions. This allows fluid communication of the primary brake circuit with the primary brake fluid reservoir of the braking system via the bore and allows fluid communication of the secondary brake circuit with the secondary brake fluid reservoir of the braking system via the bore, as is known to those skilled in the art.
What is needed is an improved brake apply master cylinder.